Risk achievement worth is one of themostwidely utilized importancemeasures. RAWis defined as the ratio
of the riskmetric value attained when a component has failed over the base case value of the riskmetric. Traditionally,
both the numerator and denominator are point estimates. Relevant literature has shown that
inclusion of epistemic uncertainty (i) induces notable variability in the point estimate ranking and (ii) causes
the expected value of the risk metric to differ from its nominal value. We investigate the conditions under
which the equality of the nominal and expected values of a reliability risk metric holds. We then study
howthe presence of epistemic uncertainty affects RAWand the associated ranking.We propose an extension
of RAW(called ERAW)which allows one to obtain a ranking robust to epistemic uncertainty.We discuss the
properties of ERAWand the conditions under which it coincides with RAW. Weapply our findings to a probabilistic
risk assessment model developed for the safety analysis of NASA lunar space missions.

Risk achievement worth is one of themostwidely utilized importancemeasures. RAWis defined as the ratio
of the riskmetric value attained when a component has failed over the base case value of the riskmetric. Traditionally,
both the numerator and denominator are point estimates. Relevant literature has shown that
inclusion of epistemic uncertainty (i) induces notable variability in the point estimate ranking and (ii) causes
the expected value of the risk metric to differ from its nominal value. We investigate the conditions under
which the equality of the nominal and expected values of a reliability risk metric holds. We then study
howthe presence of epistemic uncertainty affects RAWand the associated ranking.We propose an extension
of RAW(called ERAW)which allows one to obtain a ranking robust to epistemic uncertainty.We discuss the
properties of ERAWand the conditions under which it coincides with RAW. Weapply our findings to a probabilistic
risk assessment model developed for the safety analysis of NASA lunar space missions.